Relative to the survey, this sounds promising. Currently, the remaining bottlenecks are:
1) the available surface (ideally 25 m2 for energy autonomy with my system in Europe)
2) the stirling engine availability (100-500W range): I’ve contacted many firms: Sunpower(tm) hasn’t replied, Stirling Tech(tm) has and their price is interesting but over-sized system (3700 W), and an Indian supplier has told me that a 300W stirling engine is currently feasible in the 500-1500$ range to begin with (he has bought German designs), with a 23% heat-to-electric efficiency for a hot source around 550°C, and minimal maintenance for 24/24h operating conditions, but he is only interested by people who have a lot of cash (mass-production only), so I would need to create a firm, with all the credit-related issues, and have to put IP rights in order not to be killed in a few month by Chinese manufacturers if the product is a success (I can only afford to patent it from the start in only 3 countries (France, Germany and Spain?): for international patent, you need at least 100,000$! I would have to sell all my organs for that! )

For the concentrator itself, the design must allow a very cheap and robust system (price of the components and tracking checked), so most of the price will consist in the stirling engine as long as it is outsourced.

I need first to build a prototype, in order to at least qualify the optical quality relative to the tracking uncertainties (the concentration ratio should be around 500, so above parabolic troughs) and the heat storage system, and perform some modeling (Openfoam, blender for optics). The problem is that I live in a small flat and don’t have a lot of resources, so I wait for a friend of mine to come back, who will help me with the prototype. (he has a huge garden, resources, and experience in the commercial field)

For the product availability, hopefully this would be in mid-2011 (need time for administrative stuffs, capital-related stuffs, ordering the components, quality check and packaging). The product would be built by the buyer itself in order to cut the prices and have compact packages).